De or het montageafdeling?

The correct Dutch article is:

de montageafdeling

Rule Words ending in -ing: almost always de. See the rule

How to use montageafdeling

the montageafdelingde montageafdeling
this montageafdelingdeze montageafdeling
that montageafdelingdie montageafdeling
our montageafdelingonze montageafdeling
your montageafdelingjouw montageafdeling
every montageafdelingelke montageafdeling
which montageafdeling?welke montageafdeling?
a big montageafdeling / the big montageafdelingeen grote montageafdeling, de grote montageafdeling